The present invention relates to impact-type crushers and, more particularly, to those which utilize centrifugal force to hurl the rocks to be crushed against an impact surface.
Impact-type crushers utilizing centrifugal force to hurl rocks to be crushed are generally known. For example, in U.S. Pat. No. 4,126,280, issued Nov. 21, 1978, to Burk, rock is fed into a rotating impeller which hurls the rock against a plurality of anvils disposed in a ring concentric with the axis of rotation of the impeller. As another approach, U.S. Pat. No. 3,970,257, issued July 20, 1976, to McDonald et al., a rotating impeller throws the rock against a bed of crushed rock instead of the anvils.
In either case, a primary design consideration is providing for a sufficient useful life span of the apparatus, particularly those portions of the apparatus which come in contact with the rock as it is hurled. For example, portions of the device, such as impeller vanes and upper and lower plates within the impeller, as subject to a great deal of wear while they are accelerating the rock. As a result, any portions of the apparatus subject to wear require periodic replacement, which necessitates substantial down time for the equipment and incurs considerable cost for replacement of worn parts.
Of course, in an anvil-type crusher, such as that shown in Burk, the wear problem is very severe on the anvil surfaces, since the rock is specifically directed thereagainst as it is hurled. In general, therefore, it is preferred to use crushers of the rock bed-type, such as shown in McDonald et al., since the high cost and inconvenience of replacing worn anvils can be avoided.
Notwithstanding the foregoing disadvantage of anvil-type crushers, there are circumstances in which it is desirable to use a crusher of this type. For example, a specific type of rock can be thrown against an anvil surface at a much lower speed and yet achieve comparably satisfactory results to what is possible when the rock is thrown against a rock bed. As a result, energy requirements to rotate the impeller are much less. This can be an advantage where sufficient horsepower for impeller rotation is not available, or in cases where energy is available only at great expense. As another example, where the objective in using the crusher is to provide broken faces on the rock particles rather than a reduction in their size, an anvil-type crusher will yield superior results. Additionally, certain materials may require the hard anvil surface to obtain adequate crushing.
It will readily recognized from the foregoing that an operator of a crusher may have occasions in which use of an anvil-type crusher rather than a rock bed-type crusher is preferable, or vice versa. To obtain the respective advantages of the two types of crushers, it has heretofore been necessary to purchase two different machines, which represents a substantial financial inventment. In addition, the cost to maintain two different crushers is quite substantial.
What is needed, therefore, is a crusher which can be converted from an anvil-type to a rock bed-type or vice versa. Such a conversion must be relatively simple to perform, and must involve relatively few parts. In addition, the crusher must be capable of achieving acceptable performance in either configuration.